Remote meter reading method and apparatus

ABSTRACT

A remote meter reading system has equipment at a telephone company office coupled by modems to a utility company computer which issues requests for customer data. Telephone test trunks are used to access individual meter sites and initiate meter readings using a number of single frequency bursts. Meter sending units emit a pulse for each unit of consumption and a microprocessor counts the pulses in RAM to derive separate meter readings. When interrogated, the microprocessor outputs the readings in a binary coded decimal format to a DTMF tone generator which emits each decimal number as a tone pair which is transmitted via the telephone line and is detected at the telephone company, translated into ASCII code and transmitted by modem to the utility computer.

FIELD OF THE INVENTION

This invention relates to the method and apparatus for automatic meterreading by telephone and particularly to meter data encoding method andapparatus for remote meter reading.

BACKGROUND OF THE INVENTION

It is generally desirable for utility companies to collect meter readinginformation from homes or commercial establishments without visuallyinspecting every meter at its resident location. The traditional laborintensive collection system is too expensive to be maintained and theaccuracy of the data collected is subject to considerable error. Anumber of proposals for remote meter reading have been made and somehave been put into operation. One system which has been tried uses aradio link with the meter and a mobile radio unit which is driven aroundselected neighborhoods to collect data from local meters. This requiresmanned operation of the mobile units and thus is a compromise which usesless labor than the traditional data collection method. Still anothersystem for remote meter reading uses telephone communication between theutility company and the meters to be read. The present inventionpertains to this category.

Telephonic meter reading systems have long been proposed withoutcommercial success although in recent times there has been a renewal ofcommercial attempts which seek to capitalize on improving telephonecommunication technology. In general, these systems incorporate a modemin each residential unit to receive interrogation signals from thetelephone line and to formulate and transmit meter readings via thetelephone line to the utility company. Such modems have come intowidespread use for telephone communication and are characterized by twotraits: they are expensive and unreliable as communication devices. Eventhough a modem might accurately produce signals representing the data tobe transmitted, the signals are in such a form that, due to noiseinterference or limited system fidelity, they are not faithfullytransmitted over normal telephone lines. Some systems use communicationdevices which may not be recognized as modems, yet the transmissionreliability is questionable. Some representative patented systems aredescribed below.

The U.S. Pat. No. 3,842,218 to DeLuca et al describes a system forremote meter reading by telephone which uses a modem (FIG. 5) at themeter site for initiating the interrogation of meters upon receiving acommand signal and generating a series of tones to communicate the meterconsumption information. The meters have decades supplying signals onten lines to the tone generator which yields data in decimal form.

The U.S. Pat. No. 3,868,640 to Binnie et al discloses a remote meterreading system using telephony. In one version using a frequencydivision multiplex basis, a unit at the meter site has four tonedecoders and an interrogation signal comprising up to four simultaneousfrequencies is evaluated by the unit for prompting a response. Inanother version using a time division multiplex basis, a single tonedecoder is used and the interrogation signal comprises a binary codemade up of a series of single frequency tones each representing a "1" or"0". In either version the unit responds by transmitting the meterreadings in the form of a series of tones of the same frequency.

The U.S. Pat. No. 3,842,206 to Barselotti et al shows a remote meterreading system having a meter unit which transmits meter readings as aserial binary pulse train. Each bit in the pulse train comprises eitherof two frequencies representing a "1" or "0".

The U.S. Pat. No. Re. 26,331 to Brothman et al discloses a remote meterreading system having a unit at the meter site for transmitting a codedmeter reading in the form of a modulated AC signal in one version or inthe form of serial binary pulses interspersed with synchronizationpulses in another version.

U.S. Pat. No. 4,587,536 to Oliver et al granted Mar. 25, 1986, disclosesa meter reading system including interface means between the meter andtelephone line for sending AC signals to the central office in responseto an interrogation signal. Plural multiplexers are provided at thecentral office for multiplexing the signals between a group of telephonelines and central office. A computer selects a multiplexer and one ofthe telephone lines and a continuous DC and AC coupling is establishedto the telephone line during on-hook conditions. The interface meansgenerates DTMF signals corresponding to the meter reading value whichare transmitted over the telephone line to the central office.

The Lumsden U.S. Pat. No. 4,388,690 granted June 14, 1983, discloses anautomatic meter reading transponder. The transponder includes a CPUconnected to a receiver and transmitter and a real time clock isconnected to the CPU. The CPU receives the input pulses representativeof electric power consumption. The RAM of the CPU has a plurality ofaddressable registers wherein the CPU equates each register sequentiallywith a predetermined time period. Each register contains a count whichis representative of the power consumed during the associated timeperiod.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide an inexpensivemeter reading and data transmitting apparatus for a telephonic automaticmeter reading system.

It is another object of the invention to provide an exceptionallyreliable method of meter reading and telephonic data transmission.

The invention is also carried out in a remote meter reading systemhaving telephone communication of meter data by a meter telephone unitcomprising; terminals for connection to a telephone line, means coupledto the terminals for initiating a meter reading operation, control meansfor acquiring data and furnishing data in response to initiation ofmeter reading, and a DTMF tone generator coupled to the terminals and tothe control means for receiving the data from the control means and forproducing a set of tone pairs representing the data for transmissionover the line.

In accordance with this invention, an improved transponder is providedfor use in an automatic meter reading system of the type which utilizesthe telephone system for transmission of meter readings. The transpondercomprises a microprocessor including a read/write memory. A meter pulsegenerating means is coupled with a meter and produces a meter pulsecorresponding to a unit of measurement. The microprocessor is normallyin a quiescent mode and is switched to an active mode in response to ameter pulse. The microprocessor is programmed to count pulses and tostore the pulse count in the read/write memory and to switch themicroprocessor to the quiescent mode after the pulse count is stored. Adetecting means detects a control signal on the telephone line and themicroprocessor is switched from the quiescent mode to an active mode inresponse to the control signal. The microprocessor is programmed toproduce a tone generator signal for a DTMF tone generator in response toreceipt of a control signal. The tone generator produces a sequence oftone pairs representing a pulse count stored in the read/write memoryand the microprocessor is switched to the quiescent mode after thesequence of tone pairs is produced.

Further, in accordance with the invention, the transducer is powered bysupply voltage on the telephone line except when a fault occurs on theline or the telephone is off-hook and then it is powered by a battery inthe transducer which supplies an auxiliary supply voltage. Battery poweris conserved and yet the integrity of pulse counting is assured bymaintaining the microprocessor in the quiescent state except when ameter pulse is generated. Further, battery power is conserved byutilizing for meter pulse generation a Wiegand sensor which requires nopower supply.

A more complete understanding of the invention may be obtained from thedetailed description that follows taken with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an automatic meter reading systemincorporating a meter unit according to the invention;

FIG. 2 is a schematic circuit diagram of the meter unit according to theinvention;

FIG. 3 is a diagrammatic showing of a meter sending unit;

FIG. 4 is a representation of a Wiegand type sensor in the sending unit;

FIG. 5 is a flow chart representing a part of the control program of themicroprocessor; and

FIG. 6 depicts storage registers in the RAM of the microprocessor.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A remote meter reading system is intended to provide the various utilitycompanies with a cost effective and timely method of collecting billinginformation. Integrity of the collected information is of paramountimportance. By using telephony as the data collection medium, a systemis available for nearly every utility customer. The utility companyneeds special equipment at its central office for interfacing with thetelephone company equipment as well as equipment at each home, businessor other meter site for automatically collecting meter data. Byproviding suitable flexibility in the equipment, other functions such astamper detection and remote disconnect can be provided.

Referring now to the drawings, there is shown an illustrative embodimentof the invention in an automatic meter reading system wherein thetransmission of meter reading data from the meter site is initiated byan interrogation signal from the telephone company. It will beappreciated, as the description proceeds, that the invention is alsoapplicable in a meter reading system wherein the transmission of meterreading data is initiated by a suitable unit at the meter site. It willbecome apparent to those skilled in the art that the invention may bepracticed in many different forms and may be utilized in a variety ofapplications.

As indicated in FIG. 1, the system is distributed among the utilitycompany, the telephone company and the customers of the utility company.The customer has an incoming telephone line 10 connected to aconventional telephone 12 and to a transponder comprising a residentialservices unit 14 (RSU) and one or more sending units 17. Each sendingunit is coupled with a utility meter 16. The telephone 12 may be thesame telephone used by the telephone company subscriber for conventionalvoice communication over the telephone system. The telephone company hasa test trunk 18 which is provided for the purpose of accessingindividual telephone lines without ringing the phones to test lineresistance and other aspects of the telephone equipment. This same testtrunk is used to access the individual RSU's 14 to carry out meterreading and related functions. The test trunk 18 is connected to thecustomer lines 10 through a switch 22 and a main distribution frame 24.The telephone company also houses a utility access unit (UAU) 26 whichis connected to the test trunk 18 through a subscriber access unit (SAU)28 and is connected to the utility company through a modem 30. The UAU26 accepts requests from the utility, obtains data, and transmits thedata to the utility. The (SAU) 28 accesses customer RSU's 14 over thetest trunk 18 when commanded by the utility access unit 26. The utilityhas a computer or terminal 32 coupled through a modem 36 to thetelephone company modem 30.

The meter reading system interrogates the RSU 14 at each meter site andcommunicates meter data to the utility company computer for billingpurposes without interfering in any way with the customer's service. Theutility computer 32 requests meter readings using account numbers ortelephone numbers; this communication is over the dial-up network usingcommercial modems 36, 30. In response to the request the UAU 26instructs the SAU 28 to access the customer RSU 14 via the test trunk 18(i.e., without ringing). The SAU 28 will not access the customer'stelephone line if it is in use (busy). Also the RSU 14 incorporates a"busy detect" function that causes the system to release the linewhenever the customer picks up the telephone. The SAU 28 commands theRSU 14 to transmit meter readings, reset registers, etc., by sending acontrol signal including a command signal comprising a sequence ofsingle frequency tone bursts on the telephone line. The RSU 14 respondswith DTMF (dual tone multifrequency or "touchtone" signalling) to theSAU 28. Data communicated from the RSU to the SAU is checksummed toensure data integrity. Following command execution, the RSUautomatically assumes a quiescent mode. The SAU has a digit receiverwith frequency selective filters to detect the DTMF tones. The DTMF datareceived from the RSU is translated into ASCII and sent to the UAU whichforwards it to the utility computer 32. The SAU communicates with theUAU in ASCII format using serial RS232C protocol.

The system is designed to work with commonly used meters of the ordinaryunencoded type or the encoded type. Appropriate meter interfaces orsending units are provided as separate assemblies to provide flexibilityin packaging as well as the ability to accommodate a large number andvariety of meters. Unencoded meters may have magnetic pickups added. Thesending units make all meters compatible with the RSU 14 and all metersare read in the same manner. In particular, the sending unit issues avoltage pulse to the RSU for each unit of consumption. In accordancewith this invention, a special sending unit is provided, as will bedescribed subsequently.

The RSU 14 shown in FIG. 2 has a line interface comprising tip and ringterminals for connection to the telephone line 10 and a diode bridge 40having its input connected to the terminals and its output connected toground and a positive line 44. A 250 volt zener diode 46 is connectedacross ground and line 44 for transient suppression. The bridge assuresthat the voltage output is independent of the telephone line 10polarity. The nominal voltage into the terminals is 48 volts. The line10 furnishes power to the RSU.

A voltage regulator 48 and power switch circuitry furnish a regulatedvoltage Vcc. A 24 volt zener diode 50 and a resistor 51 couple thepositive line 44 to the collector and base of a transistor 52 while theemitter is coupled to the collector and base of a transistor 53 which isconfigured as a 14 volt zener diode connected at one side to ground. Apair of Darlington connected transistors 54, 55 have the input baseconnected to the resistor 51, their collectors connected to the anode ofthe diode 50 and their output emitter connected through four seriallyconnected diodes 56, 57, 58 and 60 to the input of the regulator 48. Theregulator has a terminal connected to ground and capacitors 61 and 62are connected between the regulator 48 input and output, respectively,and ground. The elements 50 through 60 drop the 48 volt input voltage toapproximately 11.5 volts for input to the voltage regulator whichmaintains an output Vcc of a constant 5 volts.

A tone selective filter, comprising a capacitor 63 and an inductor 64,is serially connected between the line 44 and ground have a junctionpoint connected to the base of a transistor 68. The filter is tuned tothe control signal frequency of 1633 Kh.

For backup purposes a 9 volt lithium battery 70 maintains continuedoperation of the RSU when telephone line power is not available to theinput of the voltage regulator 48. This occurs when there is a failureof voltage supply on the telephone line and also when the telephone isoff-hook as will be described subsequently. The battery 70 is connectedbetween ground and the input of the regulator 48 through a diode 74. Aslong as there is power from the telephone line 10, the voltage at theregulator 48 input is higher than the voltage at the anode of the diode74 and all power will be supplied by the line 10. When the telephoneline is removed or the voltage drops below 24 volts the diode 74 willconduct to supply battery power to the regulator 48.

A low battery detect circuit includes an operational amplifier 80; italso provides a voltage divider 82 and a transistor 84 serially coupledbetween the battery 70 and ground. A zener diode 86 is connected betweenan input of the operational amplifier 80 and the collector of thetransistor 84 to provide a reference voltage at the operationalamplifier when the transistor 84 is turned on. The transistor 84 isnormally turned off, creating approximately the same voltage on allinputs of the operational amplifier 80 keeping it turned off. Power isturned on to the operational amplifier only when the transistor 84 isturned on to obtain a reading and then a reference voltage is placed onone input of the operational amplifier. The voltage on the other input(derived from battery voltage) is compared to the reference voltage andwhen the battery voltage is low the output of the operational amplifieris low.

A processor 100 such as a COP840C microprocessor is coupled to thecircuitry described above. It is also coupled to meters 16 and otherinputs through a multiplexer 102 (MUX) such as a CD4512B multiplexer andto a DTMF tone generator 104 such as a TP5088 generator which transmitsthe RSU output data. The processor 100 includes a RAM, i.e., aread/write memory, and is operated under control of a program stored inits ROM. The processor 100 has ports GND and Vcc for power supplyconnection, clock ports CKI and CKO connected to a crystal 106 for clockinput, a port G1 connected to the base of transistor 84 to turn on thelow battery detect circuit, and a port 13 connected to the output ofoperational amplifier 80 to receive the low battery signal. Processorports L0 through L4 are connected to inputs of the tone generator 104.Ports L0, L1 and L2 are also connected to the selector ports A, B and Cof the multiplexer 102. The multiplexer has one data output port whichis coupled to port I1. A RESET port activates the processor when avoltage is applied to the port through a transistor 120. A latching portD0 coupled to the base of the transistor 120 can be energized by theprocessor to latch the RESET on. A port I2 is connected to a voltagedivider 121 which is connected to the junction of diodes 58 and 60 tosense the presence of voltage at that point. The normal voltage is 4.2volts and is limited to 5.7 volts maximum by a clamping circuitincluding a diode. The voltage is lost if the line voltage goes belowthe 24 volt level of the zener diode 50. When the telephone is offhook,i.e. in use, the reduced voltage on the telephone line will be blockedby zener diode 50 and the voltage at port I2 will be at logic low andthis prevents port D3 from going high. This in turn, prevents any tonegenerator output.

As shown in FIG. 2, there are four meter sending units 17 in theillustrative meter reading system. Each sending unit 17 is associatedwith a different meter, the meters being numbered 1, 2, 3 and 4. Each ofthe meter sending units is of a special type which requires no powersupply and has no moving parts. It is well adapted for retro fitting onexisting meters, especially the conventional water meter and gas meterwhich use a separate rotary hand indicator or number wheel indicator foreach decimal digit in the reading. The sending unit uses a Wiegandsensor which is commercially available from the Sensor EngineeringCompany of Hamden, Conn. The principles and structure of the Wiegandsensor are disclosed in Wiegand U.S. Pat. No. 3,820,090 granted June 25,1974 and Wiegand U.S. Pat. No. 4,247,601 granted Jan. 27, 1981. TheWiegand sensor utilizes a bistable ferromagnetic wire of generallyuniform composition having a central magnetically soft core portion andan outer magnetically hard shell portion with relatively low and highcoercivity respectively. The shell portion is permanently magnetized andoperates to magnetize the core portion in a first direction (the"confluent state") in the absence of an external magnetic field. Themagnetization of the core portion is reversible by the application of anexternal magnetic field so that the core and shell have oppositepolarity (the "reverse state") when the external field is removed themagnetization of the core is changed to the first direction by theeffect of the shell portion. Thus, by manipulating the external magneticfield excursions, the shell and core can be switched to the confluent orreverse states of magnetic polarity. The polarity switching occursabruptly. For use as a pulse generator, a sensing coil is wrapped aroundthe Wiegand wire and the sensor comprises a two wire device thatrequires no power. The sensing coil develops signal pulses of two orthree volts in magnitude and twenty microseconds in duration and canoperate with a pulse rate up to twenty KHz. It is suitable for very lowspeed operation as well and is operable over a wide range oftemperature.

A meter sending unit 17 is shown diagrammatically in FIGS. 3 and 4. FIG.3 shows a typical meter such as a gas meter with a panel 130 having fivedifferent dial indicators of the rotary hand type, each different handrepresenting a different digit in the meter reading. The handrepresenting the least significant digit is replaced with a rotarytwo-pole permanent magnet 134 and a Wiegand sensor 136 is disposedadjacent the rotary magnet. The Wiegand sensor 136 and the rotary magnet134 are shown in FIG. 4. The Wiegand wire 138 is wrapped with a sensingcoil 142. The rotary magnet wheel 134 is located so that its magneticfield is effective to switch Wiegand wire from the confluent state tothe reverse state and allows it to switch back to the confluent state asit rotates through one revolution. Accordingly, meter pulses ofalternate polarity are generated in the coil 142 as shown in thewaveform diagram of FIG. 4.

The sensor of each meter sending unit 17 is coupled through a meterinterface circuit with the input of the multiplexer 102, as shown inFIG. 2. The interface circuit comprises a transistor 110 having its baseconnected through a resistor to the output terminal of the Wiegand wiresensor. The diode across the base bypasses the negative pulses and thepositive pulses are effective to turn on the transistor 110. Thecollector of the transistor is connected with one of the input ports X1,X2, X3 or X4 of the multiplexer 102. The collectors are also coupledthrough a large resistor 111 to the base of the transistor 120 so thatas a pulse, at ground potential, is applied to the multiplexer by ameter sending unit, a similar pulse turns on the transistor 120 toactivate the processor 100.

The data input ports of the multiplexer 102 are selectively coupled tothe port I1 of the processor. The four meter sending units 17 arecoupled through individual signal conditioning circuits 108, asdiscussed above, to one of the input ports X1, X2, X3 or X4 of themultiplexer 102. The command signal issued by the SAU is transmittedover the telephone line as a sequence of tone bursts at 1633 Hz. Thissignal is derived from the filter capacitor 63 and inductor 64 andapplied through transistor 68 to the input port X0 of the multiplexer.The input at port X0 is at logic low during each tone burst. A tamperdetector terminal is coupled through a transistor 122 to the data inputport X6 of the multiplexer. When the terminal is grounded, the input atport X6 is at logic high. DTR terminals DTR 1, 2 and 3 are provided forconnection to an installers portable field unit to initialize registersin the processor and perform tests at the time of installation. Theterminals DTR 2 and 3 are connected to input ports I0 and G0respectively on the processor for receiving and transmitting data,respectively. The terminal DTR 1 is coupled through a resistor andconductor 124 to the port X5 of the multiplexer. These other inputs,like the meter sending units 17, are coupled to the base of thetransistor 120 through resistors 111 to activate the RESET when a pulseoccurs. The multiplexer 102 operates under control of the processor 100to provide the input signals to the processor as they occur and, if morethan one occurs simultaneously, to present them in a prescribed order.When a pulse occurs it is applied to a multiplexer input and alsothrough the transistor 120 to activate the processor. The processor thensweeps through a series of seven 3 bit codes, one for each MUX input,applying them to the multiplexer via ports L0, L1 and L2. When the codematches a MUX input at ground potential an output pulse is sent to theport I1 of the processor. The processor acts on the pulse according toits source.

The processor 100 has a port D3 coupled to the base of a transistor 112which connects Vcc to the tone generator 104 to supply power thereto. Tosupply data to the tone generator the processor energizes a tone enableoutput port L4 and a four bit data output at the ports L0 through L3.The tone generator, in turn has an output port coupled to the base of atransistor 114 which is connected to modulate the load current on thetransistors 54 and 55.

In operation the RSU is powered by the telephone line 10 but the powerrequirements are extremely small. The RSU has a very high inputimpedance (at least 5 megohms) during idle state. Except when receivinginputs or when interrogated by the SAU, the processor 100 remains in thequiescent or halt mode and draws less than 1 microamp. When a pulse isemitted by a sender 17, the multiplexer 102 receives the pulse on inputport X0, X1, X2 or X3 and the RESET port of the processor receives alogic high input to activate the processor. Similarly when a commandsignal, tamper signal or DT signal is received on input ports X0, X5 orX6, the processor is activated. The processor sends a sequence of 3 bitcodes to the MUX which operates to serially couple to the processor portIl any input pulses which are present on the inputs of the MUX whentheir corresponding codes are received from the processor on the MUXports A, B and C. When a meter pulse is emitted by a sender 17, theprocessor responds to the pulse by incrementing a count in RAM at anaddress reserved as a register for the meter identified by theparticular code. The registers in RAM are depicted in FIG. 6 as R1, R2,R3 and R4, corresponding to meters 1, 2, 3 and 4, respectively. Then theprocessor returns to the halt mode and awaits another event. Informationis stored in a similar manner for the tamper detection or installationinput. Thus the processor itself serves as the data storage medium forthe meter reading and other data. When it is time to report the data tothe utility company no search or interrogation of the sources of thedata, such as the meters, is required. The command signal tones receivedfrom the telephone line are presented to the processor in the same way.The operation as described above is performed by the processor undercontrol of the program stored in ROM. The relevant part of the controlprogram is represented by the flow chart of FIG. 5.

When the SAU issues a control signal via the telephone line, it does soby a series of tone bursts at a frequency of 1633 Hz. The initial tonesignal is an alert signal. The initial or alert signal, if acknowledged,is followed by command signal which identifies the meter number. Thenumber of tone bursts in each signal is the code for a particularfunction. The filter 63, 64 passes that tone to the transistors 68 and120 which, in turn, pass it to the multiplexer 102 and to the RESET portof the processor. The multiplexer 102 passes the tone to the processorport Il as described above. After determining that a tone is present theprocessor will keep itself activated by supplying the latching signalfrom the port D0. The processor verifies the frequency by monitoring thelevel transitions of the tone. The frequency verification is performedby the processor under program control as represented by the flow chartof FIG. 5. If the frequency is incorrect, the processor will turn off,otherwise, the processor will turn on the tone generator 104 throughtransistor 112 by resetting port D3. Then the generator outputs anacknowledge burst in the form of a DTMF tone pair which is a mix of twopreset frequencies. The tone pair modulates the load current drawn bythe RSU via the transistors 114, 55 and 54 and that modulation is sensedby the SAU and decoded. Then a command signal of 1, 2, 3 or 4 requeststhe reading of the corresponding meter.

When a meter reading is requested the processor outputs a series ofdigits to the tone generator 104. The DTMF protocol provides 8 fixedfrequencies combined in 16 tone pairs representing the decimal digitsand six other characters. The meter reading, as accumulated in thecorresponding register in the processor RAM, is output in a binary codeddecimal format. Each decimal digit is represented by a four bit codewhich is translated by the tone generator into a tone pair unique to thedigit value. The meter reading is accompanied by other data which isoutput as a series of DTMF tones representing decimal digits. Tonesrepresenting other characters are used for the message header andterminator. The complete response is typically as follows: messageheader (1 digit), meter type (2 digits), customer account number (8digits), wake command echo (3 digits), meter reading (10 digits), tamperindication (1 digit), error code indication (2 digits), checksum value(3 digits), and a message terminator (1 digit). The tones are 70 to 90msec long and are separated by pauses of the same length.

A busy detection function is provided by the 24 volt zener diode 50.When a telephone is taken offhook, the voltage across the tip and ringterminals drops to 24 volts or less. At this level the diode 50 inhibitsinput current and no voltage is present at the port I2 of the processorwhich prevents any tone output.

Tamper indication is used to recognize an event such as opening the RSUhousing or disconnecting the wires. When such an event is detected anappropriate flag is set in the processor and is read out along with themeter reading.

It will thus be seen that the invention provides an inexpensive remotemeter reader which produces data outputs for telephone transmission withthe highest integrity, operates at extremely low power levels, and isflexible to perform auxiliary functions as well.

Although the description of this invention has been given with referenceto a particular embodiment, it is not to be construed in a limitingsense. Many variations and modifications of the invention will now occurto those skilled in the art. For a definition of the invention referenceis made to the appended claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. In an automatic meterreading system of the type which utilizes a telephone system having acentral office, multiple subscriber lines each having a subscribertelephone connected therewith at a subscriber station, said subscriberlines being coupled to a switch in the central office for selectiveconnection of any one of the subscriber lines to another line, voltagesupply means for supplying electrical power from the central office tothe subscriber lines, a test trunk for selectively accessing saidsubscriber lines without ringing the telephone of the selected line, asubscriber line access means coupled with the test trunk for accessing aselected line, a transponder at the subscriber station coupled with saidsubscriber line and with one or more utility meters, and control signalmeans coupled with the subscriber access means for generating a controlsignal for a transponder at a selected subscriber station, theimprovement wherein said transponder comprises:detecting means fordetecting a control signal on the telephone line, a microprocessorincluding a read/write memory, a meter pulse generating means coupledwith said meter for producing an electrical meter pulse corresponding toa predetermined meter event, first coupling means for coupling the meterpulse generating means to the microprocessor, means for switching themicroprocessor from a quiescent mode to an active mode in response to ameter pulse, the microprocessor being programmed to count pulses fromsaid meter pulse generating means and for storing the pulse count insaid read/write memory, and for switching the microprocessor to thequiescent mode after the pulse count is stored, a DTMF tone generatorcoupled with the microprocessor, second coupling means for coupling saiddetecting means to said microprocessor, and means for switching themicroprocessor from a quiescent mode to an active mode in response to acontrol signal, said microprocessor being programmed to produce a tonegenerator signal for said tone generator in response to a predeterminedcontrol signal for producing a sequence of tone pairs representing saidpulse count stored in the read/write memory and for switching themicroprocessor to the quiescent mode after the sequence of tone pairs isproduced.
 2. The invention as defined in claim 1 wherein:saidtransponder has a pair of terminals connected respectively with the tipand ring conductors of said telephone line whereby said transponder isnormally energized from said voltage supply means from the centraloffice, and modulating means for modulating the current on saidtelephone line, said DTMF tone generator has an output coupled with saidmodulating means for modulating the current in said telephone line atthe frequencies of the tone pairs.
 3. The invention as defined in claim2 wherein:the pulse count stored in said read/write memory is formattedas a sequence of binary coded decimal numbers, and the DTMF tonegenerator generates a unique tone pair for each number, whereby thepulse count is transmitted as a sequence of tone pairs.
 4. The inventionas defined in claim 1 wherein:said first coupling means comprises amultiplexer circuit and a reset circuit each having an input coupledwith the meter pulse generating means, the reset circuit having anoutput coupled to a reset input of the microprocessor for switching themicroprocessor from a quiescent mode to an active mode in response to ameter pulse and for switching it to a quiescent mode after theoccurrence of a meter pulse, the microprocessor has means forinterrogating a multiplexer when in an active mode to identify whichmeter issued said pulse, and means responsive to said pulse forincrementing a pulse count register in the read/write memorycorresponding to the identified meter.
 5. The invention as defined inclaim 1 including:a movable magnetic member carried by said meter andwhich is cyclically movable along a path having a length correspondingto a predetermined unit of measurement, and a Wiegand sensor having anoutput coil coupled therewith for producing an output voltage pulse whenthe magnetic state of the Wiegand sensor is switched from one polarityto the other, said sensor being disposed adjacent to said path forgenerating a voltage pulse in response to movement of said magneticmember past said sensor.
 6. The invention as defined in claim 5 whereinsaid transponder further comprises:a voltage regulator for energizingsaid transponder and having an input coupled with the subscriber linefor receiving a supply voltage, a battery for producing an auxiliarysupply voltage, and means for switching the auxiliary supply voltage tothe input of the voltage regulator when the supply voltage on thesubscriber line falls below a predetermined value due to a fault on saidsubscriber line or due to said telephone going offhook whereby saidtransponder continues to accumulate the pulse count from said meter. 7.The invention as defined in claim 1 wherein:said control signal iscomprised of a tone of predetermined frequency, and said processor isprogrammed for determining whether the frequency of the control signalis equal to said predetermined frequency, and to switch the processor tothe quiescent mode if it is not said predetermined frequency.
 8. For usein a meter reading system using a telephone line for communication ofmeter data, a transponder comprising:detecting means for detecting acontrol signal on the telephone line, a microprocessor including aread/write memory, a meter pulse generating means coupled with saidmeter for producing an electrical meter pulse corresponding to apredetermined meter event, first coupling means for coupling the meterpulse generating means to the microprocessor, means for switching themicroprocessor from a quiescent mode to an active mode in response to ameter pulse, a microprocessor being programmed to count pulses from saidmeter pulse generating means and for storing the pulse count in saidread/write memory, and for switching the microprocessor to the quiescentmode after the pulse count is stored, a data signal generator coupledwith the microprocessor, second coupling means for coupling saiddetecting means to said microprocessor, and means for switching themicroprocessor from a quiescent to an active mode in response to acontrol signal, said microprocessor being programmed to cause said datasignal generator to transmit encoded data representing the pulse countstored in the read/write memory in response to a predetermined controlsignal and for switching the microprocessor to the quiescent mode afterthe encoded data signal is transmitted.
 9. The invention as defined inclaim 8 wherein:said first coupling means comprises a multiplexercircuit and a reset circuit each having an input coupled with the meterpulse generating means, the reset circuit having an output coupled to areset input of the microprocessor for switching the microprocessor froma quiescent mode to an active mode in response to a meter pulse and forswitching it to a quiescent mode after the occurrence of a meter pulse,the microprocessor has means for interrogating a multiplexer when in anactive mode to identify which meter issued said pulse, and meansresponsive to said pulse for incrementing a pulse count register in theread/write memory corresponding to the identified meter.